As previously mentioned, monoclonal IgG antibodies generated from joint-derived B cells of RA patients have actually a strong bias toward citrullinated autoantigen recognition [25], and AID-expressing follicular units from RA synovium xenotransplanted into SCID mice are associated with circulating human IgG ACPA in mouse sera [66]. This evidence concerns the gene AICDA and rheumatoid arthritis.